Quote:
Originally Posted by Steve C.
It's not the tightness of the lash, it's the velocity of the cam at that point that dictates how hard the lifter hits the cam. You can have a cam designed for a looser lash that has less velocity at the lash point then a cam designed for a tight lash.
Source: http://speedtalk.com/forum/viewtopic.php?t=8265
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I'm not convinced that statement is 100% correct, I know from experience with our race car, that when the springs were getting to the end of their life (borderline valve float going through the traps) if we tightened the lash up a few thou from the .028/.030" recommended by the cam manufacturer it would help at least finish the race weekend, which leads me to believe that less lash reduces lifter bounce.
When it comes to requiring more spring pressure on the hybrid set-up vs. running a hyd. roller lifter with all things the same and
no more rpm is being sought with the solid roller lifters there's no reason why more spring pressure is required (lots of smart people at Comp Cams and other cam companies, but there seems to be a lot less smart people answering tech questions a lot of the time and you can call and talk to 10 different people and get 10 different answers). I did a back to back, same day dyno test with a 246/252 .400" lobe lift hyd. roller cam in a 468ci engine swapping from hyd. to solid roller lifters and there was no indication of valve float turning the engine up to 6200-6300rpm, using the 99893 springs set up around 1.800". The solids showed 6-8 more hp over the hyd. above the torque peak. Maybe if we backed the lash way off there might be something there, but until I actually see some solid back to back data to prove that the solid lifters need more spring pressure I'm just not buying it.
Valve, retainer and spring weight all have to be taken into consideration when figuring out how much spring pressure is required for an application along with how aggressive the cam lobe is and how much rpm the engine needs to turn to optimize the combo.